I learnt from my former classmates that they used to eat food like chocolates because It boost your mind. But my suggestion is, study before the test not the exactly before one day and make sure that you understand the concept so that you will not get confused on every side of a certain topic. Lastly, if you are really having hard time then maybe you should focus on the key words so that it will make you easy to remember them. I've suggested it because I works on me, I hope it will work on  you too.